This invention relates to copper and optical fiber cables having a filling material within their core, and more particularly to a filling material that exhibits excellent thermal oxidative stability. More particularly, this invention relates to copper and optical fiber cables having a core in which a composition of matter, which is grease-like and exhibits excellent thermal oxidative stability fills interstices in the core.
In the cable industry, it is well known that changes in ambient conditions lead to differences in water vapor pressure between the inside and the outside of a plastic cable jacket. This generally operates to diffuse moisture in a unidirectional manner from the outside of the cable to the inside of the cable. Eventually, this will lead to an undesirably high moisture level inside the cable, especially if a plastic jacket is the only barrier to the ingress of the moisture. High levels of condensed moisture inside a cable sheath system may have a detrimental effect on the transmission characteristics of a metallic conductor cable.
Furthermore, water may enter the cable because of damage to the cable, which compromises its integrity. For example, rodent attacks or mechanical impacts may cause openings in the sheath system of the cable to occur, allowing water to enter, and, if not controlled, to move longitudinally along the cable into splice closures.
Copper and optical fiber cables have made great inroads into the communications cable market. Although the presence of water itself within a copper and optical fiber cable is not necessarily detrimental to its performance, passage of the water along the cable interior to connection points or terminals or associated equipment inside closures, for example, may cause problems especially in freezing environments and should be prevented.
Consequently, it should be no surprise that cables for transmitting communications signals must meet industry standards with respect to waterblocking provisions. For example, one industry standard requires that there be no transmission of water under a pressure head of one meter in one hour through a one-meter length of cable.
Waterblocking materials have been used to fill cable cores and to coat portions of cable sheath systems to prevent the movement longitudinally thereof of any water which enters the cable. Although the use of such a material, which typically is referred to as a filling material and which typically is in the form of a grease-like composition of matter, causes housekeeping problems for field personnel during splicing operations, for example, it continues to be used to prevent entry of the water into the core. In copper and optical fiber cables, a further important function of a filling material is the maintenance of the copper and optical fibers in a low stress state.
A grease-like composition of matter typically is a semisolid or semi liquid substance comprising a thickening or gelling agent in a liquid carrier. The gelling agents used in greases frequently are fatty acid soaps, but high melting point materials, such as clays, silica, organic dyes, aromatic amides, and urea derivatives also are used. Nonsoap thickeners are typically present as relatively isometric colloidal particles. All types of gelling agents form a network structure in which capillary forces hold the carrier.
When a low stress is applied to a grease-like material, the material acts substantially as a solid. If the stress is above a critical value, then the material flows and the viscosity decreases rapidly. The decrease in viscosity is largely reversible because it is typically caused by the rupture of network junctions between the filler particles, and these junctions can reform following the release of the critical stress.
A cable filling material, especially a copper and optical fiber cable filling material, should meet a variety of requirements. Among them is the requirement that the physical properties of the cable remain within acceptable limits over a rather wide temperature range e.g., from about xe2x88x9240.degree. to about 76.degree. C. It is desirable that the composition of matter of the filling material be substantially free of syneresis, i.e. have an ability to retain uniform consistency, over the temperature range. Generally, syneresis is controlled by assuring dispersion of an adequate amount of colloidal particles or other gelling agent.
Of particular importance, is the thermal oxidation resistance of the grease-like compositions in order to maintain the foregoing physical characteristics to meet the requirements set forth above.
U.S. Pat. No. 6,160,939 discloses an optical cable having a filling material with stable viscosity and yield stress wherein the filling material comprises 80-95 wt % of synthetic oils; 5-20 wt % of a diblock copolymer and less than 1.5 wt % of an inorganic gelling agent; and 1-2 wt % of a high molecular weight hindered phenolic antioxidant. An acceptable antioxidant is stated to be Irganox 1035 available from Ciba Specialty Chemicals Corporation, preferably 0.3 wt % of Irganox 1035 antioxidant is used in combination with 1.7 wt % of Irganox 1076 antioxidant, the latter constituent being used to prevent the antioxidant from settling out. Alternatively, 2 wt % of Irganox 1076 antioxidant or Irganox 1520 antioxidant is suitable and available from Ciba Specialty Chemicals Corporation. Irganox is a registered trademark of Ciba Specialty Chemicals Corporation. U.S. Pat. No. 5,905,833 discloses these antioxidants for use in a similar cable filling material.
U.S. Pat. No. 4,701,016 discloses a thixotropic grease composition for cable applications wherein Irganox 1010 antioxidant is employed in the examples in an amount of 0.2 pbw.
U.S. Pat. No. 5,276,757 teaches that any thermal oxidative stabilizer that is capable of functioning as a thermal oxidative stabilizer in the instant filling compositions is suitable so long as it is no more than monofunctional with respect to participation in hydrogen bonding with the fumed silica in the fumed silica network. The preferred thermal oxidative stabilizer is Irganox 1076. The data in Tables 1 and 2 therein suggest that Irganox 1035 results in crosslinking producing negative impacts on both the critical yield stress and the oil separation of optical fiber cable filling compositions.
U.S. Pat. No. 5,728,754 discloses that antioxidant and antioxidant mixtures can be used in the filling materials, which are usually the primary hindered phenol type including various derivatives of phenols, used either solely or in combination with phosphite or thioesters. A mixture of Wingstay SN-1 and Wingstay L-1 is used in the examples.
U.S. Pat. No. 4,105,619 discloses that antioxidants normally used with polyolefin cable fillers are also useful in the cable filling composition and include organic phosphates, phenols, thiodipropionate, BHT; BHA and the like. Preferred is a mixture of thiodipropionate ester, an organic polyhydric phenol and an organic phosphate disclosed in U.S. Pat. No. 3,255,136 and sold under the trademark Mark 2047 of Witco Chemical Corporation.
U.S. Pat. No. 4,757,100 discloses a cable filling composition wherein all the examples contain up to 25 wt % antioxidants, i.e. mixtures of Irganox 1035, 1010 and 1024 with triphenylphosphine.
Surprisingly, it has been found that the combination of (a) sulfur containing primary phenolic antioxidant; (b) a mixture of mono- and di-alkyl butyl/octyl diphenylamine; (c) an organic phosphite or phosphonite and (d) optionally one or more hindered phenol antioxidants is especially effective towards providing oxidative stability for the filling material for copper and optical fiber cables.